Byte order-large-end byte order and small-end byte order

Basic byte order

 

 

For a single byte (A byte), Most processors process bits in the same order, so the storage method of a single byte is generally the same as the transmission method.

For multi-byte data, such as integers (4 bytes in 32-bit machines), there are two main storage methods for different processors. The storage method of 0x0a0b0c0d in memory is used as an example, the following methods are available:

Note:0xThe prefix indicates the hexadecimal format.

Big client Sequence

The big-Endian sequence is also called the Big-Endian sequence.

Data in 8 bits

 

 

In the example, the highest valid bit (MSB, most significant byte) is0x0aStored at the lowest memory address. Next byte0x0bThere is a later address. It is similar to the reading order of hexadecimal bytes from left to right.

Small client order

The smallest Order (English: Little-Endian) or the smallest tail order.

• Data in 8 bits:

Address growth direction →
...	0x0d	0x0c	0x0b	0x0a	...

The minimum valid bit (LSB, least significant byte) is0x0dStored at the lowest memory address. The next byte is followed by the address.

• Data in 16 bits:

Address growth direction →
...	0x0c0d	0x0a0b	...

Minimum 16-bit unit0x0c0dLow storage.

• Change the address growth direction:

When you change the address growth direction from right to left, the table is more readable.

Growth direction of the ingress address
...	0x0a	0x0b	0x0c	0x0d	...

The minimum valid bits (LSB) is0x0dStored at the lowest memory address. The next byte is followed by the address.

Growth direction of the ingress address
...	0x0a0b	0x0c0d	...

Minimum 16-bit unit0x0c0dLow storage.

Method for judging the big end and small end: # Include <stdio. h> </P> <p> int main (INT argc, char * argv []) <br/> {<br/> int I = 1; <br/> char * P = (char *) & I; <br/> If (* P = 1) <br/>{< br/> printf ("small-end mode "); <br/>}< br/> else <br/> {<br/> printf ("big end mode "); <br/>}</P> <p> return 0; <br/>}</P> <p>Char is a byte. Therefore, to forcibly point the char type P to I, P must point to the lowest address of I. Then, you can determine whether the value in P is 1 to determine whether it is a small end. Network order

Network Transmission generally adopts the big-End sequence, which is also calledNetwork byte order, OrNetwork order. In the IP protocol, the large client order is defined as the network byte order.

Berkeley Socket API defines a set of conversion functions for 16 and 32-bit integers in the network order andLocal byte order. Htonl and htons are used for local sequence conversion to network sequence; ntohl and ntohs are used for network sequence conversion to local sequence.

# Define ntohs (n) // network byte order to host byte order n Represents net, H represents host, s represents short # define htons (N) // host byte order to network byte order n Represents net, H represents host, s represents short # define ntohl (n) // network byte order to host byte order n Represents net, H stands for host, L stands for long # define htonl (n) // host byte order to network byte order N stands for net, H stands for host, L stands for long references: [1] bytes